John Churchill was perhaps the greatest military genius who ever fought for England, and certainly the best general since Cromwell's day. Far superior to William III as a general, he was fully his equal in keeping together ill-assorted and jealous allies. In a day of generally static methods of warfare, with siegecraft predominating, Marlborough injected a boldness and originality into strategy, and on the battlefield his keen mind and quick eye seemed always to pick out the best tactical movements. It was not only as a strategist and battle tactician that he excelled. If genius is "the capacity for taking infinite pains," he qualified for that highest distinction. No small part of his success came from his meticulous foresight for every detail: his soldiers always had food, clothing, shelter, and pay, and came to the battlefield in the pink of condition.
(from A History of England and the British Empire)